There is an extensive history of the use of histocultured tumor samples for use in prognosis of tumor development and as a tool for predicting responsiveness to drugs. These histochemical techniques, which are the basis of histoculture drug response assay (HDRA™), have an extensive literature. The general features of this technique are described, for example, in a recent paper by Singh, B., et al., Head and Neck (2002) 24:437-442. As described in this paper, briefly, biopsied tissue is washed and cut into 1 to 2 mm3 fragments and placed onto 0.5 cm2 pieces of collagen sponge-gel (Gel Foam, Pharmacia & Upjohn, Inc.) in equal quantities. The sponge-gel cultures are then placed into DMEM/Ham's F12 medium with 10% fetal calf serum and gentamicin (50 μg/ml). The cultures are then incubated for 24 hours at 37° C. and 5% CO2. Modifications of this technique are also permissible, provided the three-dimensional nature of the sample is preserved.
It has now been found that in addition to their usefulness as prognostic and drug-screening tools, such cultures are also useful as sources for messenger RNA as a substrate for expression profiling. This is significant in view of the problems associated with providing reliable expression libraries, in particular when derived from patient samples where extraction of high-quality, non-degraded RNA is difficult in view of the necrotic areas present in tumors and in view of the need to transport tumor tissue from a treatment or diagnosis center to a laboratory capable of performing the profiling analysis. By maintaining non-necrotic portions of the tumor in a three-dimensional histoculture, the expression profile of the tumor in situ is effectively preserved.